Many of β-lactam antibiotics including amoxycillin, ampicillin and cephalosporin are produced by using, as a starting material, a fermentation product obtained by culturing bacteria such as those belonging to the genera Penicillium and Cephalosporium. 
For example, for producing 6-aminopenicillanic acid (6-APA) or 7-aminocephalosporanic acid (7-ACA), which is the most important intermediate for the industrial production of a semisynthetic penicillin and cephalosporin, by cleaving an amide bond (deacylation) of penicillin G (PenG), penicillin V (PenV) or cephalosporin C, penicillin G acylase (benzyl penicillin amide hydrolase, also called penicillin G amidase, EC 3.5.1.11) has commercially been used. This enzyme is also used industrially for converting phenylacetyl-7-aminodeacetoxycephalosporanic acid, which is chemically produced from PenG generally, into 7-aminodeacetoxycephalosporanic acid (7-ADCA). Semisynthetic penicillins and cephalosporins produced by chemical synthesis reactions between these β-lactam cores 6-APA, 7-ACA and 7-ADCA with side chain compounds form an important market of β-lactam antibiotics.
Enzymes which have been conventionally useful in deacylation for producing the β-lactam core are classified as hydrolysis enzymes, and usually called “acylase” or “amidase” in said field. Among these acylase enzymes, ones recognizing a β-lactam antibiotic as a substrate are further specified as “β-lactam acylases”. In the β-lactam acylase activities, there are hydrolysis (deacylation) activity in the case where an acyl group is detached by water, and transfer activity catalyzing transfer of an acyl group from an activated side chain substrate into a nucleophilic substance as a reverse reaction. This chemical form is represented by the following general formula. That is, in the compound acceptable as a substrate by a specific acylase: X—CO—NH—Y, the characteristics of said chemical forms X and Y are defined according to the substrate specificity of the correspond acylase. X represents a side chain, and Y represents an acyl acceptor group. For example, in the case of PenG, X—CO— represents a phenylacetyl side chain, and —NH—Y represents 6-APA. These β-lactam acylases attract attention for having possibility to convert an acyl group transfer reaction process from a chemical synthesis method to an enzyme method in producing β-lactam antibiotics, but they have not been put into practical use yet due to their poor production efficiencies.
β-lactam acylases are classified as follows according to the substrate specificity and molecular characteristics (Process Biochemistry, 27, 131, 1992, World J. Microbiology & Biotechnology, 10, 129, 1994). β-lactam acylases are broadly classified into penicillin acylases and cephalosporin acylases. Penicillin acylases are further classified into penicillin G acylases, penicillin V acylases and ampicillin acylases. Cephalosporin acylases are further classified into cephalosporin acylases and glutaryl-7-ACA (GL-7-ACA) acylases.
Penicillin G acylases, which have been commercially used for producing 6-APA, etc., form heterodimers consisting of a small subunit (α: 16 to 26 kDa) and a large subunit (α: 54 to 66 kDa). On the other hand, penicillin V acylases are known to form tetramers of a subunit having a molecular weight of 35 KDa, and ampicillin acylases are known to form homodimers having a molecular weight of 72 kDa. Moreover, from their substrate specificities, some of them have the name of α-amino acid hydrolases, but these cases are also included in the above acylase activity for the chemical reaction form.
Among these acylases, acylase gene sequences of the microorganisms coding for penicillin G acylase have been clarified. That is, there are Escherichia coli (Nucleic Acids Res., 14 (14), 5713, 1996), Kluyvera citrophila (Gene, 49, 69, 1986), Alcaligenes faecalis (Japanese Kokai Publication Hei-4-228073), Providencia rettgeri (DNA seq., 3, 195, 1992), Arthrobacter viscosus (Appl. Environ. Microbiol., 54, 2603, 1988), Archaeoglobus fulgidus (Nature, 390, 364, 1997), Bacillus megaterium (FEMS Microbiol. Lett. 125, 287, 1995), and the like. Moreover, as for GL-7-ACA acylase having a heterodimer structure, Pseudomonas sp. (J. Ferment. Bioeng., 77, 591, 1994) is clarified, and as for cephalosporin acylase, Pseudomonas sp. (J. Bacteriol., 163, 1222, 1985, J. Bacteriol., 169, 5821, 1987), etc. have been clarified.
Since these are clarified at the DNA levels as gene families, gene clonings are easy, and the DNA acquisition by carrying out screening by a method using an enzymatic activity of a microorganism genome library as the index is also easily possible.